The Calvin cycle is a series of biochemical reactions that occur in the stroma of chloroplasts in plants. It is part of the process of photosynthesis, where plants convert carbon dioxide from the atmosphere into glucose. The cycle uses energy from ATP and NADPH, produced in the light-dependent reactions, to drive the conversion of carbon dioxide into organic compounds. During the Calvin cycle, carbon dioxide is fixed into a five-carbon sugar called ribulose bisphosphate (RuBP) by the enzyme RuBisCO. This process produces a three-carbon compound, which is then converted into glucose and other carbohydrates. The cycle repeats multiple times to produce enough sugar for the plant's energy needs.